Internal combustion engines include one or more combustion chambers, each equipped with a piston connected via a connecting rod to a crankshaft. Combustion of fuel in the combustion chamber causes the piston to move in one direction within the combustion chamber, rotating the crankshaft. Rotation of the crankshaft in turn helps to drive the piston in an opposite direction within the combustion chamber. The piston typically includes annular grooves on its side wall. The grooves accommodate annular piston rings that separate the side wall of the piston from the inner walls of the combustion chamber.
During operation of the engine, some of the fuel or fuel-air mixture in the combustion chamber may enter the circumferential gap between the piston side wall and the combustion chamber inner wall. When the fuel or fuel-air mixture in the combustion chamber ignites, a flame front travels away from the location where the combustion initiated, consuming the fuel or fuel-air mixture in its path. The piston and the combustion chamber walls tend to conduct some of the heat released because of the combustion. Because of this heat loss, the flame front may not enter the gap between the piston side wall and the combustion chamber inner wall, leaving the fuel and/or fuel-air mixture trapped in the circumferential gap unburned. The unburned fuel or fuel-air mixture may exit the combustion chamber with the exhaust gases.
The fuel that remains unburned and escapes from the combustion chambers does not participate in combustion, reducing the efficiency of the engine. Additionally, the escaping unburned fuel contributes to the total amount of undesirable emissions produced by the engine. Although the unburned fuel may be combusted in an after-treatment device to prevent its discharge to the atmosphere, implementing these devices adds to the cost of operating the engine. Therefore, it is desirable to reduce the amount of unburned fuel that is discharged from the combustion chamber into the exhaust leaving the combustion chamber.
One technique for reducing the amount of unburned fuel in the combustion chamber is disclosed in Canadian Patent Application No. 2863036 A1 to Huang et al. (“the '036 application”) that published on Oct. 29, 2014. The '036 application discloses a piston that has a chamfered edge extending from the top surface of the piston to the outer side surface. The '036 application discloses that the chamfer angle and the chamfer depth may be selected so as to reduce the amount of unburnt hydrocarbons, carbon monoxide, and NOx in the exhaust. The '036 application further discloses that although the amounts of unburned hydrocarbons and carbon monoxide decreased with the chamfered piston, the amount of NOx increased for all chamfer designs. In addition, the '036 application discloses that the amount of unburned hydrocarbons in the combustion chamber increased for some chamfer designs as compared to the unchamfered pistons.
Although the '036 application discloses the use of a chamfered piston to reduce the amount of unburned hydrocarbons in a combustion chamber, the disclosed piston may still not be optimal. In particular, the disclosed piston results in an increase in the amount of NOx. Moreover, for at least some chamfer geometries, the disclosed piston caused an undesirable increase in the amount of unburned hydrocarbons in the combustion chamber. It is likely that in these cases the shape of the chamfer did not allow the flame front to advance into the gap between the piston side wall and the inner wall of the combustion chamber.
The engine piston of the present disclosure solves one or more of the problems set forth above and/or other problems in the art.